High pressure laminates are laminated articles typically made of a plurality of core sheets, a decor sheet and an overlay sheet. The sheets are coated with lamination polymers which are typically thermosetting materials, such as melamine or phenolic resins.
The core sheets are made from unbleached kraft paper and are dark in color. The number of core sheets used depends on the application requirements, i.e. strength and environment, and the desired thickness of the laminate. Laminates have a thickness ranging from 0.030 to 0.090 inch. The core sheets are typically saturated with phenolic resins.
The decor sheets are typically made of very heavy paper comprised of cellulose fibers and an opacifying pigment such as titanium oxide. The decor sheets are printed upon with designs to create the decorative pattern of the laminate. The decor sheets are typically saturated with melamine resins.
The overlay sheets are clear cellulose sheet which act as a protective layer over the decor sheet. These sheets are usually saturated with melamine resins. The overlay sheets are used optionally depending on the need for protective surfaces.
In a typical process for preparing laminates, the sheets are saturated with the appropriate thermoset resins and then stacked. Next they are placed in a press and subjected to temperatures of about 150.degree. C. and pressures of about 1100 to 1200 psi for a particular period of time. However, during processing the resins release volatiles causing environmental concern. The melamine resins typically release phenolic volatiles and the phenolic resins release formaldehyde volatiles.
The laminates that are produced are thermoset products due to the nature of the resins employed in the process. For flat surface applications irreversibility after formation and cure creates no problems. However, some applications have curved surfaces and require that the laminates be flexible to allow for a tailored fit in a particular place. This property is known in the industry as postformability and is measured by the inch radius of the bend of the laminate in the postforming unit. The smaller the radius achievable without cracking, the better the postformability. The current industry standard is 0.25 inch radius which provides only minimal flexibility.
Postformability is obtained by only partially curing the laminates prior to application. The partially cured state creates some flexibility in the laminates. After fitting the laminates in place, full cure is completed by the application of heat. Once fully cured the laminate is set and cannot be adjusted. Thus if mistakes are made, the laminates must be discarded and replaced resulting in considerable material waste and higher costs.
Thus, there exists a need in the art for a high pressure laminate that does not release any volatiles during processing, that has more flexibility providing for a wider range of applications, and that remains adjustable after full cure.